15.9 is too high for a low-end price. I was offered a C9 Brown Bomber (priced at 15, I believe) on my Beams Modest a few days ago. After I turned the offerer down, he apparently went on to trade it for a Scorching CM (which happens to be either the original of the one you have, or the dupe. Either way.) http://www.tf2outpost.com/user/445388 is a link to his trade history.

This means your low-end can't be right - it's either 15 or 14.1, depending on whether it was offered on the CM or whether the CM was offered on it. Those rejected offers aren't doing you any favors either. I've been offered (and turned down) similar but better offers (I was offered a sulphurous non-robo modest, and in separate offers a 1 of 1 Darkblaze robo-modest and a 1 of 2 Hellfire robo-modest, both with sweeteners). In fact, this could imply that people see the CM as having less value than a beams modest, priced at 14.